This invention relates generally to optical waveguides on substrates, and more particularly to a method of preventing metal wires from oxidizing during high temperature glass formation on metalized substrates.
Applicant incorporates by reference herein its previous U.S. Pat. application filed on Jun. 29, 1990 entitled "Apparatus and Method of Forming Optical Waveguides on Metalized Substrates" which has been granted U.S. Pat. No. 5,059,475. Also incorporated by reference herein is Applicant's previously filed U.S. Pat. Application Ser. No. 07/779,959 entitled "Optical Waveguide of Silica Glass Film on Ceramic Substrate." Flame hydrolysis deposition ("FHD"), a process which involves the deposit of powdered glass on a substrate and its subsequent fusion for consolidation into a solid glass at high temperatures, has been used to deposit waveguides for optical signal transmission on substrates. Other deposition methods such as chemical vapor deposition ("CVD") and sputtering have also been used to form optical waveguides on substrates.
Electronic IC chips are normally bonded to ceramic substrates to form either single chip or multi chip electronic modules. Connecting two Or more chips on a Ceramic substrate is accomplished with wires Thus, the term metalized ceramic substrate is derived from the metal wires which are embedded in the substrate connecting the electronic devices. It is desirable to be able to integrate optics and electronics on the same substrate. One manner of doing this involves the formation of glass waveguide layers onto a surface of a metalized ceramic substrate.
The formation of the glass layers on the substrate requires high temperatures in the range of 1200.degree.-1700.degree. C. These high temperatures coupled with the oxygen in the surrounding atmosphere tend to cause the metal wires in the substrate to oxidize. With the present invention, metal wires will be saved when layers of silica glass are formed onto the ceramic substrate to form planar optical waveguides.
The waveguide forming process of FHD is followed by high temperature consolidation during which the metal wires on the substrate surfaces or imbedded in the substrate come under attack by the oxygen impurity in the consolidation furnace. Oxidation of the wires can cause a breakage in electrical signal and power transmission.
The present invention is designed to inhibit oxidation of the metal wires during the formation of silica waveguides on the substrate. The present invention protects the metalized substrates during the consolidation phase. In the method of the present invention, a carbon plate of any applicable geometry or shape is placed adjacent the metalized substrate to attract oxygen molecules approaching the substrate. The oxygen molecules will tend to react with the carbon plate first so that the metal wiring (such as copper, molybdenum, and tungsten and any other less reactive metallurgy) will be safe from oxidation during the high temperature consolidation phase.
The present invention involves the formation of optical waveguides on ceramic substrates such as AL203. Electronic or opto-electronic (0-E) IC chips may be bonded to the substrate, after the waveguides are formed. The optical waveguides perform as optical interconnects between electronic and 0-E chips. Therefore, the present invention is useful in making opto-electronic devices for communication and computer applications.
The method of the present invention is useful in applying a glass film on a substrate to be used as an optical waveguide. The glass film may be deposited directly onto the substrate or onto a coating on the substrate. Thin film, thick film, and multilayer ceramic (MLC) substrates can have these glass films deposited thereon to form waveguides and integrated optical circuits.
The foregoing and other objects and advantages of the invention will become more apparent when considered in view of the accompanying drawings and the following description